(1) Field of the Invention
The present invention relates to an apparatus and method for controlling valve timing of an engine, constructed such that a rotation phase of a cam shaft with respect to a crank shaft is variably controlled continuously by oil pressure control using a valve.
(2) Description of the Related Art
Heretofore as an apparatus for controlling valve timing of an engine, there is a vane type valve timing control apparatus such as disclosed in Japanese Unexamined Patent Publication No. 10-141022.
With this apparatus, recess portions are formed on an inner peripheral face of a cylindrical housing secured to a cam sprocket, while vanes of an impeller secured to a cam shaft are accommodated in the recess portions, the construction being such that the cam shaft can rotate relatively with respect to the cam sprocket, within a range in which the vanes can move inside the recess portions.
Furthermore, the construction is such that by supplying and discharging oil pressure relatively with respect to a pair of hydraulic chambers (advance angle side hydraulic chamber and delay angle side hydraulic chamber) formed by the vanes partitioning the recess portions into front and rear in the rotation direction, the vanes are maintained at a central position of the recess portion, and continuously variable control of the rotation phase is performed. Moreover, the construction is such that once the oil pressure in the pair of hydraulic chambers has been adjusted to an oil pressure to give a target rotation phase, an oil pressure passage is closed by a valve so that the supply and discharge of oil pressure is stopped.
However, a positive and negative rotational torque (referred to hereunder as cam torque) is alternately generated in the cam shaft due to valve springs urging the intake and exhaust valves in the close direction, and when the oil pressure passage is closed by the valve so that the supply and discharge of oil is stopped, the oil pressure in the hydraulic chamber on the side to which the positive cam torque is applied increases.
Then, if oil leakage occurs due to the increase in oil pressure due to the cam torque, when the positive and negative of the can torque inverts, air is drawn in from the position where the oil leakage occurs so that air is mixed with the oil in the sealed hydraulic passage.
If a cam torque is applied in the condition with air mixed, since the compressibility of air is greater than that of oil, then when a positive cam torque is applied, the rotation phase is displaced further. Hence there is the possibility that with normal feedback control, convergence is not possible, and hunting of the rotation phase occurs.
The present invention takes into consideration the above problems with the object of providing a control apparatus and control method which can prevent beforehand excessive hunting of the rotation phase due to cam torque, and which can reliably converge hunting of the rotation phase due to cam torque.
In order to achieve the above objectives, the present invention is constructed so that supply and discharge of oil pressure in a hydraulic chamber is forcibly performed in preference to a control for making a rotation phase coincide with a target value. Due to this forcible supply and discharge of oil pressure, mixing of air inside the hydraulic passage is prevented and any mixed air is discharged.
The forcible supply and discharge of oil pressure to the hydraulic chamber may be performed by forcible offset of an oil pressure control signal, this forcible offset being performed in a condition with oil pressure maintained.
Furthermore, the offset amount in the offset of the control signal may be variably set based on a target value of the rotation phase, a temperature of the operating oil, rotation speed of the engine, or supply pressure of the operating oil.
On the other hand, the construction may be such that the forcible supply and discharge of oil pressure in the hydraulic chamber is performed when the amplitude of the rotation phase is above a predetermined value. The condition where the amplitude of the rotation phase is above a predetermined value may be judged from an actually measured rotation phase. Moreover, the construction may be such that a condition is judged where it is predicted that the amplitude of the rotation phase will reach above a predetermined value.
For the condition where it is predicted that the amplitude of the rotation phase will reach above a predetermined value, a condition where the temperature of the operating oil is above a predetermined temperature, or the oil pressure supplied to the hydraulic chamber is below a predetermined value may be judged.
The forcible supply and discharge of oil pressure when the amplitude of the rotation phase is above a predetermined value may be performed by forcibly changing the target value of the rotation phase.
In changing the target value, preferably the target value is changed to a maximum advance angle or a maximum delay angle. Furthermore, the construction is more preferable such that after changing to either one of the maximum advance angle side and the maximum delay angle side, changing is then to the other side.
Moreover, the forcible changing of the target value is preferably performed in a high load and high rotation speed region of the engine, or in a decelerating operating condition.
Other objects and aspects of the present invention will become apparent from the following description of embodiments, with reference to the appended drawings.